This invention relates to a magnetic particle-type electromagnetic coupling apparatus, and more particularly to an improved electromagnetic coupling apparatus which is cooled by heat pipes.
A magnetic particle-type electromagnetic coupling apparatus employs magnetic particles to transmit torque between a drive rotor and a driven rotor. Magnetic particles are disposed between opposed surfaces of the drive rotor and the driven rotor. When the magnetic particles are not magnetized, the drive rotor and driven rotor can rotate freely with respect to one another, but when the magnetic particles are magnetized by an external magnetic field, the magnetic particles become substantially a solid mass and can transmit torque from the drive rotor to the driven rotor. Therefore, if the two rotors are rotatably supported, an electromagnetic coupling apparatus can be employed as a clutch, while if one rotor is free to rotate while the other is held stationary, it can be used a braking mechanism for the rotating member.
During the operation of a magnetic particle-type electromagnetic coupling apparatus, slippage may take place between the magnetic particles and the surfaces of the drive rotor and driven rotor which the particles contact. Due to this slippage, a great deal of frictional heat is generated, and if this heat is not somehow removed, the magnetic particles and the rotors will reach an extremely high temperature. In addition to possibly damaging the rotors, this high temperature may cause the magnetic particles to become sintered through oxidation, as a result of which they lose their ability to function as a coupling medium. Accordingly, a magnetic particle-type electromagnetic coupling apparatus is equipped with a cooling device for cooling the magnetic particles and the surfaces of the rotors to prevent an excessive rise in temperature.
For example, Japanese Published Utility Model No. 51-49478 discloses an electromagnetic coupling apparatus in which a coolant such as water or oil is made to circulate through an annular coolant passageway formed within a drive rotor. The coolant is supplied to the drive rotor from an external coolant supply via coolant supply passageways formed in a drive shaft which is connected to the drive rotor. After the coolant is circulated once through the coolant passageway, it is returned to the coolant supply. However, that apparatus has the disadvantages that it requires an external coolant supply and a pump to circulate the coolant. Furthermore, because of the necessity of forming coolant passageways in the drive rotor and the drive shaft, these members are difficult and expensive to manufacture. In addition, the apparatus requires periodic maintenance to prevent the leakage of the coolant. It therefore has a number of serious drawbacks.
An alternative means of cooling an electromagnetic coupling apparatus is a heat pipe. Japanese Published Utility Model No. 60-510 discloses a magnetic particle-type brake having a heat pipe which extends longitudinally from the center of a drive rotor. However, as heat is generated along the outer periphery of the drive rotor, the centrally-located heat pipe is too far remote from the source of heat to provide any significant cooling effect.
Japanese Utility Model Laid-Open No. 57-181934 discloses an electromagnetic coupling apparatus which employs two heat pipes, one of which is embedded in the center of a drive rotor and the other of which is embedded in the center of a driven shaft. However, even though the heat pipes are disposed near the source of heat, because the heat pipes are embedded, they must have small dimensions and the areas of the surfaces through which heat exchange takes place are accordingly small, so that an adequate cooling effect can not be obtained.